cloth simulation, cloth(plane) collide at center of of the cube instead of at the surface
This can be because if many problems you should try these:-
Make sure that all modifiers on cube are applied and that on plane the cloth simulator is the last modifier or is only equipped with cloth modifier.
Also increase permeability of collision modifier on the cube as 1 and check that it is setted to volume rather than being on object origin.
Also try deleting and again adding the cube in the file it is not working.
If it still don't work then you may even delete the plane and add it again in your scene.